1. Field of the Invention
This invention generally relates to a bushing. More specifically, the present invention relates to a resin bushing used for a dampening mechanism.
2. Background Information
A clutch disk assembly or dampening disk assembly used for a clutch of a car has a clutch function of coupling and/or uncoupling a flywheel of the engine to the transmission shaft, and a dampening function of absorbing and dampening torsion vibrations transmitted from the flywheel. The clutch disk assembly basically includes a clutch disk, a pair of input plates, a hub and an elastic portion. The pair of input plates is fixedly coupled to the clutch disk. The hub is disposed on the inner circumferential side of the input plate. The elastic portion elastically couples the hub and the input plates together for movement in a rotary direction. The elastic portion is disposed between the input plates and the hub, and is compressed in a rotary direction when the input plate rotates relatively against the hub. When the clutch disk assembly is coupled with the flywheel, a torque is inputted to the input plates of the clutch disk assembly from the flywheel. The torque is transmitted to the hub via the elastic portion, and then is outputted to a shaft extending from a transmission. When a torque fluctuation is input to the clutch disk assembly from an engine, a relative rotation is caused between the pair of input plates and the hub, and the elastic portion is compressed repeatedly in a circular direction.
In addition, the clutch disk assembly typically includes a friction mechanism. The friction mechanism is disposed between the input plates and the hub, and generates a friction resistance when the input plates rotate relatively against the hub. The friction mechanism includes basically a plurality of washers and urging portions.
A clutch disk assembly of a separated hub type has a hub flange (separated flange) in which a conventional flange of the hub is separated from a boss. In addition, in the clutch disk assembly of a separated hub type, the boss and the hub flange are coupled in a rotary direction by an elastic portion with a low rigidity. The clutch disk assembly has a wide torsion angle between the input plate and the hub, and shows a two step rigidity (low rigidity and high rigidity).
The conventional clutch disk assembly of a separated hub type described above includes, for example, a small friction mechanism between a retaining plate (one of a pair of input plates) and the boss of the hub, and a large friction mechanism between the retaining plate and the hub flange. The large friction mechanism includes a first friction portion and a first urging portion. The first friction portion touches the hub flange, and is also connected with the retaining plate in a relatively non-rotatably and axially movably manner. The first urging portion is disposed between the first friction portion and the retaining plate, and urges the first friction portion toward the hub flange side. The small friction mechanism includes a second friction portion and a second urging portion. The second friction portion touches the flange of the hub and is also connected with the retaining plate in a relatively non-rotatably and axially movably manner. The second urging portion is disposed between the second friction portion and the retaining plate, and urges the second friction portion toward the flange side. Generally, the first friction portion is set to have a friction coefficient larger than that of the second friction portion. The first urging portion is set to have an urging force larger than that of the second urging portion. Consequently, the large friction mechanism generates a friction (high hysteresis torque) larger than that of the small friction mechanism.
When the hub flange rotates relatively against the hub within a range of a torsion angle of a first step, an elastic portion with a low rigidity is compressed, and the second friction portion of the small friction mechanism rubs the flange of the boss, resulting in characteristics of low rigidity and low hysteresis torque. After the hub flange starts rotating together with the boss in a body, a relative rotation is caused between the hub flange and the pair of input plates. Within the range of this second step, the elastic portion with a high rigidity is compressed between the hub flange and a pair of input plates, and the second friction portion of the large friction mechanism rubs the hub flange, resulting in a characteristic of a high rigidity and high hysteresis torque.
A bushing made of, for example, resin is used for a dampening mechanism of a clutch disk assembly. The bushing made of a resin material can have a complicated shape easily by means of molding. Some resin bushings have a friction face to rub other portions in a rotary direction. Some bushings are connected with other portions in a rotary direction elastically via spring. In that case, the bushing has a concave part to seat the spring in, and a touching face to support both ends of the spring in a circular direction is formed at both ends of the concave part in a circular direction.
In addition, some bushings have a connecting part projecting in an axial direction in order to be connected with other portions relatively non-rotatably.
In the conventional resin bushing mentioned above, a part connected with other portions, for example, a part to support the spring and a part connected with other portions relatively non-rotatably, is easily abraded. When an abrasion progresses, a gap is caused between the bushing and other portions, resulting in unfavorable torsion characteristics.
In view of the above, there exists a need for a resin bushing which overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.